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Sate Sen. Pat Steadman votes aye during the 3rd reading on gun measures at the Colorado State Capitol in Denver on March 11, 2013. (Joe Amon, The Denver Post)

A Democratic sponsored bill that limits ammunition magazines of more than 15 rounds passed through the Senate Monday, despite some members of the party defecting and casting votes in opposition to the measure.

The bill passed on a 18-17 vote, with Democratic Sens. Cheri Jahn of Wheat Ridge and Lois Tochtrop of Thornton voting against it. Two Republican lawmakers on Monday said they will disobey the measure if it becomes law.

House Bill 1224 is originally sponsored by Rep. Rhonda Fields, D-Aurora, and passed through the House in February on a 34-31 vote.

Senators passed an amendment to the bill that bans any shotgun magazines that hold more than 28 inches of shotgun shells. Shells vary in size, and originally the bill outlawed any magazines with more than eight shells — something Republicans argued banned "common shotguns."

The measure now heads back to the House for a vote because it was amended in the Senate.

Democrats have made HB 1224 the heart of a far-reaching package of gun control laws that include universal gun backgrounds checks and the ban of online training for concealed carry handguns, which also passed through the Senate Monday.

If passed, anyone who currently possesses a magazine that holds more than 15 rounds is able to keep it, though if they transfer or sell the magazine, that individual would face a class 2 misdemeanor charge.

Manufacturers will be allowed to continue to produce the devices, though they would be required to engrave a date of production on each.

Sen. Mike Johnston, D-Denver, on Monday stressed support for the bill, saying that limiting ammunition magazines could offer enough time for a person to intervene if a gunman must stop to reload.

"And if that prevents coffins with for children then it's worth it," said Johnston, alluding to the mass shooting in Newtown, Conn., where 20 first graders and six staffers were killed in December mass shooting by a gunman using a weapon equipped with a large-capacity magazine.

Colorado Senators listen to arguments before voting on the gun measures on the floor on March 08, 2013 in Denver. (Joe Amon, The Denver Post)

Johnston was the only other Democrat besides the bill's Senate sponsor, Mary Hodge, to speak in favor of the magazine limit.

Meanwhile, Republicans have called the bill flawed and futile in quelling any future mass shootings.

"I will willfully and purposefully and civilly disobey this law," said Sen. Greg Brophy, R-Wray, a line that drew loud applause from the gallery. Vicki Marble, R- Fort Collins, joined Brophy in saying she would not obey the measure if it became law.

Sen. Steve King, R-Grand Junction, said government should not let law-abiding citizens be out gunned by criminals.